"Semimonocoque" as used herein refers to aircraft having a fuselage of the type constructed, at least in part, by attaching a veneer around forming members, such as longitudinal stringers and circumferential belt frame members, to produce a structure in which the veneer carries at least a portion of the stresses arising in the fuselage. Many modern aircraft employ a semimonocoque design, including aircraft that are equipped with on board electronic systems and aircraft that are retrofitted with new electronic systems as such systems become available.
The present invention relates to heat transfer systems that provide cooling and heat dissipation functions in semimonocoque aircraft. In one application, the present invention is used to cool electronic systems on such aircraft. Many modern electronic systems used in aircraft generate sufficient heat to destroy or interfere with the function of individual electronic components such as resistors, capacitors, transistors and integrated circuits. Consequently, heat generated by these electronic systems must be dissipated at a sufficient rate to maintain the system temperature at or below a predetermined upper operating limit, typically about 55.degree. C. (131.degree. F.) for many electronic systems. Additionally, new electronic systems must be tested prior to deployment, requiring the systems to be temporarily installed on existing aircraft. The heat load generated during testing of temporarily installed electronic systems often requires additional cooling capacity, above and beyond the design capacity of the original equipment.
Conventional air conditioning equipment is one means of cooling aircraft electronic systems. Conventional air conditioning equipment is, however, heavy, expensive, and maintenance intensive. Additionally, conventional air conditioning systems require substantial power which, in the case of an aircraft, must be obtained from the aircraft's engine(s) thereby reducing the aircraft's performance and increasing its fuel consumption. Heat transfer to the ambient atmosphere is a more efficient and considerably less expensive cooling method than conventional refrigeration methods for on board electronic systems. As a result, a number of different types of heat exchanger systems which transfer heat through an aircraft's fuselage skin have been developed.
One such alternative system uses air as a heat transfer medium and the aircraft's fuselage skin as a heat sink. Pressurized air is circulated past the aircraft's fuselage skin to dissipate heat and then recirculated to cool on board electronic system components. Such systems are known as air to air skin heat exchange systems. Air to air skin heat exchange systems, however, have several drawbacks.
Air has a low specific heat per unit volume, consequently, large temperature changes are required in air to air heat exchange systems to maintain low air flow rates. The temperature of the air entering the skin heat exchanger typically approaches the upper operating limit of the on board electronics, for example about 55.degree. C. (131.degree. F.). Preferably, the temperature of the air leaving the skin heat exchanger is as low as possible to maintain the air flow rates of the system as low as possible. Lowering the temperature of the air leaving the air to air skin heat exchanger has the inevitable consequence of decreasing the temperature differential across the fuselage skin, thus limiting the operational envelope of the system to high altitudes where frigid ambient temperatures exist. The volume of air recirculated in air to air skin heat exchange systems coupled with the low specific heat per volume of air also requires large flow passages in order to maintain a workable pressure drop through the system. These large flow passages are difficult to design and install around cramped electronics platforms where space is at a premium and also result in relatively heavy cooling systems. Adaptation of air to air skin heat exchange systems to existing aircraft thus requires extensive aircraft modifications which result in high cost and lengthy manufacturing schedules.
Moreover, the inside heat transfer film coefficient, which is usually on the order of 5 to 10 BTU/hr ft.sup.2 .sup.0 R, dictates the fuselage skin area required for air to air skin heat exchange since the exterior film coefficient is much higher, on the order of 20 to 60 BTU/hr ft.sup.2 .degree.R. Thus, air to air skin heat exchange systems are incapable of taking advantage of the available heat transfer capacity per square foot of fuselage skin area.
Other alternative systems include liquid cooling systems. The use of liquids to transfer and dissipate heat is highly utilized because fluids typically have a very high heat capacity per unit volume compared to gasses such as air. Liquid cooling systems used in aircraft typically dissipate heat collected in a liquid coolant to the fuel located in the wing tanks with coolant to fuel heat exchangers. The fuel in turn dissipates heat to the frigid atmosphere that exists at the high operational altitudes where many modern aircraft operate.
One major disadvantage of existing aircraft liquid cooling systems, which dissipate heat to the aircraft's fuel, is that such systems require extensive aircraft modification. Consequently, such systems are expensive to design and install, especially in the case where the system is retrofitted to an existing aircraft. Compounding this problem is the fact that the installation cost of existing aircraft liquid coolant systems is not proportional to the installed cooling capacity. Thus, the installation cost of a 60 kW system of the existing type could cost nearly as much as a 120 kW system. Additionally, retrofitting a liquid coolant system into an existing aircraft is time consuming, thereby reducing aircraft availability.
U.S. Pat. No. 4,819,720, issued to Howard, discloses a heat exchanger used to cool avionic equipment whereby a liner is used to create a gap with the aircraft's skin forming a heat transfer envelope through which air may be circulated.
U.S. Pat. No. 2,646,971, issued to Raskin, discloses a method for attaching a fluid transferring tube to a metal plate for transfer.
U.S. Pat. No. 4,763,727, issued to Kreuzer, et al., discloses an assembly which connects a heat conducting plate to a pipe for heat transfer.
U.S. Pat. No. 4,969,409, issued to Merensky, discloses a system for cooling food and beverages on aircraft consisting of a cold air chamber next to the skin of the aircraft.
U.S. Pat. No. 3,776,305, issued to Simmons, discloses a heat transfer system in which air flowing over a network of plates is used to cool a liquid flowing through the plates.
U.S. Pat. No. 4,057,104, issued to Altoz, discloses an electronic component pod which is mounted on the exterior of the aircraft. Components in the pod are cooled by the flow of air over the exterior surface of the pod.
U.S. Pat. No. 4,273,183, issued to Altoz, et al., discloses a unidirectional heat transfer assembly for use between an electronic assembly on an aircraft and the skin and/or pod on the aircraft. The device includes a thermal decoupler mechanism which operates to disengage a retractable interface heat transfer surface when the aircraft skin rises to a predetermined temperature.
U.S. Pat. No. 4,786,015, issued to Niggemann, discloses heat exchanger tubes that are noncircular in construction and act as a load-bearing structure for the leading edges of an air foil or the nose cone of an aircraft.
U.S. Pat. No. 4,557,319, issued to Arnold, discloses a system of heat exchanger tubes which are noncircular and are used to cool the keels of marine vessels.
U.S. Pat. No. 2,856,163, issued to Bidak, et al., discloses an arrangement for maintaining a tubing assembly in heat transfer contact with a wall.
The foregoing references, the disclosures of which are incorporated in their entireties for all purposes, do not however provide the novel modular heat exchange system of the present invention.